Dielectric heating apparatus



'se t. 12, 1950 H. R. WARREN ,5 2 87 DIELECTRIC HEATING APPARATUS Filed Feb. 27, 1948 :5 Sheets- Sheet 1 inventor ,B Henry R. Warren Horn ys Sept. 12, 1950 H. R. WARREN DIELECTRIC HEATING APPARATUS 3 SheetsSheet 2 Filed Feb. 27, 1948 I Henry R. Warren By W M/% Attorneys xx LO Sept. 12, 1950 H. R. WARREN 2,522,487

DIELECTRIC HEATING APPARATUS Filed Feb. 27, 1948 I 3 Sheets-Sheet 5 I lllllllfqgg'glll a 25 25 Ill 24 24 III 25 8 I 25 imm 28 Illfii...

54 93 53 ii H I inventor Henry R.Warre n Attorney s Patented Sept. 12, 1950 DIELECTRIC HEATING APPARATUS Henry R. Warren, Louisville, Ky., assignor to The Girdler Corporation, Louisville, Ky., a corporation of Delaware Application February 27, 1948, Serial No. 11,560

15 Claims. 1

This invention relates to dielectric heating apparatus and particularly to dielectric-heating units provided with a load tray which is retractable from a compartment of the unit for loading and unloading thereof and which is insertable into that compartment for treatment of a dielectric load disposed upon a heating electrode comprised in the tray assembly.

In accordance with the present invention, the heating electrode carried by the tray is at high potential with respect to ground to afford short, direct connection to a high-frequency tank coil in a compartment below the heating compartment and the tray electrode is supported from the tray by insulators insuring that all other parts of the tray, including exposed parts such as operating handle and the tray front, are always at ground potential: more specifically, when the tray is inserted into the heating compartm'ent for treatment of the load, the insulated tray electrode is connected, capacitively or conductively, to a high-voltage high-frequency terminal disposed within the compartment and connected to said tank coil of the compartment below.

More particularly, the high-voltage terminal may be shaped to serve as a corona shield for a feed-through insulator through which extends the connection from the tank coil and may be of such area that it affords substantial coupling to the tray electrode when the latter is in position for heating of a load carried thereby; or alternatively, the corona shield may be provided with or connected to a flexible or yielding contact which slidably engages the tray electrode when the tray is moved into the heating compartment.

The invention further resides in features of construction, combination and arrangement hereinafter described and claimed.

For a more detailed understanding of the invention and for illustration of preferred forms thereof, reference is made to the accompanying drawings in which:

Fig. 1 is a perspective view, with parts broken away, showing the loading tray, in retracted position, and associated parts of the dielectric heating unit;

Fig. 2 is a side view, partly in section, showing the relative position of parts appearing in Fig. 1 with the tray in heating position;

Fig. 3 is an end view, partly in section, of components appearing in Figs. 1 and 2;

of the invention; and

Fig. 5 is an end view of parts appearing in Fig. 4.

Referring to Figs. 1 and 2, the dielectric heating unit comprises a cabinet or housing In usually and preferably formed of sheet metal attached to and supported by a metal angle framework. The top portion of the cabinet shown comprises a heating compartment II and a compartment i2 directly below it in which is disposed the high-frequency generating equipment. The front wall of the heating compartment H is provided with an opening I3 for insertion and withdrawal of a load tray [4 with which is movable a plate I5 for supporting the dielectric load It which may, for example, consist of one or more preforms of plastic material to be preheated for disposition in a molding press upon attainment of a desired temperature.

With the loading tray in the inserted or heating position, Fig. 2, the dielectric load It is subjected to the high-frequency field between the plate l5 and an upper electrode I! disposed within'the upper portion of the heating compartment and mechanically and electrically connected to the metallic structure thereof as by the ground straps 52.

With the tray electrode I5 in the in or heating position shown in Fig. 2, it is effectively connected to the high-voltage terminal l8 supported at the upper end of a feed-through insulator I9 which is suitably secured at its lower end, as by bolts 20, to the metal partition 2| between the compartments H and [2. The lead 22 extends from terminal l8 through the insulator l9 into the lower compartment l 2; it is there connected to or forms a continuation of the high-frequency tank coil 23 whose other end or terminal is connected to the metal partition 2| or other suitable ground point. There is thus afforded a short connection from the high-potential end of the tank coil 23 to the heating electrode I5 which insures concentration of the tank-circuit inductance in coil 23. The minimizing of the lead inductance reduces the tendency for generation of oscillations at other than the desired mode of the associated oscillator. In addition, there is aiforded a more compact arrangement of the components.

The tray electrode l 5 is mechanically attached by a plurality of post insulators 24, each of which is preferably provided with corona caps 25, to the carriage 26 of the load tray Hi. The carriage 26 is guided and supported by the rail members 2'! suitablyattached to the partition 2| and may be formed of a sheet metal plate having at its rear edge a cutaway portion or slot 28 sufiiciently wide to clear the feed-through insulator l8 and sufiiciently long to permit the carriage to be pushed to its full in position, Fig. 2, without obstruction by the insulator. Preferably, as shown in Fig. 3, the rails 21 and the carriage runners are shaped to fit the ball bearings 53. Throughout the range of movement of the carriage 26, from in position (Fig. 2) to out position (Fig. l), the tray electrode l moves parallel to the plane of the upper heatin electrode ll. As the tray electrode remains horizontal during its movement, there is little tendency for the load to shift its position as the tray l4 is moved into or out of the heating compartment I I.

To facilitate and expedite loading. and unloading, the front wall 29 of the tray, which serves as a door closing the opening it of the upper heating compartment ll when the tray is in the heating position, isdropped to the position shown in Fig. i when the tray is retracted from compartment l i. As shown in Fig. l, the upper edge of the front wall 28 drops below the plane of the tray electrode l5 so that an operator may, without obstruction by the front wall 29, put preforms or other objects on the tray for heating, and remove them from the tray after heating. Moreover, preferably and as Shown, the tray 14 has no side walls which could obstruct loading or unloading. In other words, when the tray is retracted for loading or unloading, the heating electrode i5 is entirely in the clear and accessible from the front or either side of the tray.

Preferably, and as shown in Figs. 1 and Z, the front wall 28 of the tray is connected to the carriage 25 by a pair of rods or bars 30 attached at their forward ends to the front wall 29 and respectively extending through the guide blocks 3| attach d to the cabinet or housing l6 within the upper heating compartment adjacent the lower cornersoi thefront opening i3. Each. of the rods 32 is pivotally connected to the carriage 26 near the rear edge thereof; specifically, the rear end of each of the rods 30 is pivoted upon a pin 32 extending from a bearing bracket 33. The opening 34 in each of the guide blocks 39 is so shaped, Fig. 2, that as the tray I4 is pulled outwardly by the handle 35 attached to the front wall, the rods 35 pivot about the pins 32, allowing or forcing the front wall 29- to drop to the position shown in Fig. 1. Conversely, when the tray is pushed back into the. heating compartment, the blocks 3i serve as cams raising the front wall 29 to the compartment-closing position shown in Fig. 2. The guide. blocks 3| also serve as stops preventing the tray from accidentally being pulled so far forward that it would fall out of the housing and undesirably dump the load. The side bars 39, or equivalent, are below the lower electrode and, in fact, lie close to the grounded plateZB so that they are well out of the field between the electrodes l5, 51, Figs. 1 to 5, and the field between the lower electrode i5 and the terminal plate lBA, Figs. 4 and 5. With the loading tray in its heating position, Fig. 2, it is preferably provided that the rear edge thereof shall engage one or more safety switches 36, Fig. 1, which effects or, permitsenergization of the high-frequency generating equip,- ment in the lower compartment [2 of the housing. With the tray in heating position, the raised front 29 of the tray protects the operator from touching or reaching dangerously close to the tray electrode l5which is now at high potential with 4 respect to ground because of its engagement with, or proximity to, the high-voltage terminal .8, or equivalent.

As the electrode I5 is electrically isolated by insulators 24 from the carriage 26, rods 38, front panel 29 and handle 35, all of which are preferably of metal, these parts are at ground potential and may be touched by the operator without danger of injury or shock. When the tray is withdrawn from the heating compartment, the tray electrode 15 passes out of engagement with, or proximity to, the high potential terminal it, and consequently, preforms or other load objects it may be placed thereon or removed therefrom. without possibility of shocl: or injury even though the high-frequency generating equipment is not deenergized due to absence or failure of tray switches 36, or equivalent. Preferably, the front wall 29 of the tray is provided with a window 3!. suitably covered with a guard screen 38, to permit the operator at any time to view the interior of the heating compartment to check for fiashover or other evidence of improper operation.

In the form of the invention shown in Figs. 1 to 3, there is attached to the upper face of the corona-shield IS a leaf-spring contact 39 for conductively connecting the tray electrode I5 to the high-potential lead 22. As shown in Fig. 2, the free end of the springSS may pass through an opening 45 in the terminal [8 withthe tip of the spring bent to serve as a stop which limits the upward movement of the spring when the tray is retracted from the heating compartment. The other end of the leaf spring 39 may be secured by any suitable means, such as machine screws 4i, to the high-voltage terminal #8.

In the modification of the invention shown in Figs. sand 5, the leaf spring 38, or equivalent, is omitted and there is no conductive connection between the tray electrode I5 and the high-volt" age terminal supported by the feed-through insulator l8. Instead, in this modification, when the tray is. in the heating position, it, together with the high-frequency terminal 22A, forms a condenser in series with the capacity between the heating electrodes [5 and i1. Preferably, in such case, the corona shield is of suitably large area to afford'the desired coupling capacity.

In both modifications it is desirable, generally as shown in Figs. 4 and 5, to provide for adjustment of the upper, grounded electrode ll toward and away from the plane of thetray electrode l5 so to accommodate the system for heating of different loads or'to control the rate of heating. As diagrammatically shown, a knob 42. operable from the front of the cabinet l0 maybe rotated to effect raising or lowering of the grounded electrode ll. Specifically, the shaft 43 driven from knob 42 may have a threaded portion for engaging the traveling nuts 44 which pivotally support the two pairs of crossed links 45. The links of each pair are pivotally connected intermediate their ends, preferably by bar 46 which serves as the common pivot structure for both pairs of. links; The lower ends of each of the four links 45 are slidably pivotally connected to the plate I! by one of the four bearing brackets 41 provided with slots 48 for receiving the guide pins 49 extending from'links 45. The electrode H is maintained horizontal during its raising and lowering by the-guide pin 50 which extends downwardly through a closely fitting hole in the electrode H from a fixed point on the cabinet.

With the loaded tray in heating position, the operator may adjust the knob Aland during the adjustment observe through" window 31 the position of the upper electrode llwith respect to top of the load.

It'shall be understood the invention is not limited to the specific arrangements disclosed and that changes and modifications may be made within the scope of the appended claims. Features of construction involving the drop-front tray herein disclosed are claimed inco-pending application Serial No. 12,603 of a co-worker upon which has issued Letters Patent 2,497,945.

What is claimed is: I

1. Dielectric heating apparatus comprising a compartment, a first plate within said compartment and serving as one heating electrode, a high-voltage high-frequency terminal within saidcompartment and spaced from said first plate, and a load tray including a second plate movable out of said compartment to receive a dielectric load to be heated and movable into said compartment between said terminal and said first plate for cooperation with said high-voltage terminal to serve as the second heating electrode.

2. Dielectric heating apparatus comprising a compartment, a first plate within said compart'; ment and serving as one heating electrode, a high-voltage high-frequency lead, a feedthrough insulator for said lead, a corona shield spaced from said first plate for protecting said insulator and connected to said lead, and a load tray supporting a second plate movable out or said compartment to receive a dielectric load to be heated and movable into said compartment between said shield and said first plate for capacitive coupling of said second plate with said corona shield to serve as the second heating electrode.

3. Dielectric heating apparatus comprising a compartment, a first plate within said compartment and serving as one heating electrode, a flexible contact within said compartment spaced and insulated from said first plate, means for connecting said flexible contact and said first the plate to a source of high-frequency current, and

a, load tray supporting a second plate movable out of said compartment to receive a dielectric load to be heated and movable'into said compartment between said flexible contact and said first plate for engagement with-said flexible contact to serve as the second heating electrode.

4. Dielectric heating apparatus comprising a compartment, a grounded plate within said compartment and serving as one heating electrode, a high-voltage high-frequency lead, a feedthrough insulator for said lead, a corona shield spaced from said plate, mounted on said insulator to protect it and connected to said lead, a load tray slidable into and out of said compartment, a second heating electrode, insulators for mounting said second electrode for movement with said tray and for coaction with said corona shield when the tray is within said compartment to serve as the lower heating electrode.

5. Dielectric heating apparatus comprising a compartment, a grounded plate mounted within the upper portion of said compartment and serving as one heating electrode, a high-voltage highfrequency lead, a feed-through insulator in the lower portion of said compartment for said lead, a carriage slidable into and out of said compartment, a second plate supported by insulators from said carriage and movable therewith in a path between said upper heating electrode and said insulator, said second plate supporting the dielectric to be heated, and terminal means within 6 said compartment connected to said lead and cooperating with said second plate when the carriage is inserted in the compartment to establish a high-frequency electric field between said heating electrodes. i

6. Dielectric heating apparatus comprising a compartment having upper and lower walls, a first plate within said compartment and supported in spaced position parallel to the upper wall thereof to serve as one heating electrode, a high-potential lead, a feed-through insulator for said lead disposed within said compartment and supported by said lower wall, and a load tray movable into and out of said compartment comprising a frame which straddles said feed-through insulator, a plurality of insulators secured to said frame, and'a second plate -mounted upon said insulators to support the dielectric load to be treated and movable with said frame to position between said feed-through insulator and said first plate and there coacting with a terminal connected to said lead to serve as the second heating electrode.

'7. Dielectric heating apparatus comprising a compartment, a grounded plate within said compartment and serving as one heating electrode, an insulated high-voltage high-frequency terminal disposed within said compartment opposite to said heating electrode, a second heating electrode disposed within said compartment be-- tween said first heating electrode and said highvoltage terminal, and carriage means for retracting said second heating electrode from said compartment for loading or unloading of dielectric material comprising members slidably supported within said compartment and upon which are mounted insulating supports for said second heating electrode.

8. Dielectric heating apparatus comprising a compartment, a grounded plate within said compartment and serving, as one heating electrode. an insulated high-voltage high-frequency ter minal disposed within said compartment opposite to said heating electrode, a second heating electrode disposed within said compartment between said first heating electrode and said high-voltage terminal, and a load tray slidable into and out of said compartment and including said second heating electrode and insulators for attaching it to movable structure of thetray.

9. Dielectric heating apparatus comprising a compartment, a load tray movable into and out of said compartment and all of whose components including a heating electrode for supporting the load are at ground potential when the tray is retracted from the compartment, a grounded heating electrode within said compartment at one side thereof, and an insulated highvoltage high-frequency terminal disposed within said compartment at the opposite side thereof, said high-voltage terminal upon insertion of the load tray coacting with the movable heating electrode thereof to provide a high-voltage highfrequency field between said heating electrodes.

10. The combination with a metallic housing for high-frequency heating apparatus, of an upper heating electrode conductively connected to and supported by said housing, insulators, a lower electrode supported by said insulators, an opening in said housing, a load tray movable into and out of said housing through said opening and to which are attached said insulators and the lower electrode supported thereby, and a highvoltage high-frequency terminal insulated from said housing and positioned therein to be overa y said w ec d hen said 19541 new is in said housing.

11. Dielectric heating apparatus comprising a metallic housinghaving a partition between upper and lower compartments, a heat n electrode in the upper part of said upper compartment electrically connected to and supported by said housing; a terminal withinthe lower part of; said upper compartment supported by and insulated from said partition, high-frequency generating means in said lower compartment including a coil, a short direct high-potential lead from said coil to said terminal, a tray slidable intoand.

out of said upper compartment, and a second heating electrode mechanically connected to and electrically insulated from said tray for receiving a dielectric loadwhen. the tray is out oi said upper compartment and for cooperating with saidterminal when the'tray is in said upper com-- partment to: subject the load to a highefrequency field between said heat n electrodes;

4 12. Dielectric heating apparatus comprising a compartment, a high-voltage high-frequency terminal in the bottom of said compartment, a grounded upper heating electrode adjustably mounted in the top of said" compartment for movement towardand from. said high-frequency terminal, and a load tray including a lower heating electrode movable with the tray to a position between-said high-voltage terminal andsaid grounded upper heating electrode.

13. In adielectric heating apparatus, a house i s pr v d n a c m r en f ee nether inidielectric material. to-be heated, an electrode and a. terminal disposed within said housing in insulated spaced relation to-each other, means for effectively connecting said'electrode and said.

heated by an electric. field between said electrodes when said structure is. in operative position in said compartment,. and means operativev to establish electric potential on said second electrode from said terminal when. said tray structure is in its said operative position in said compartment 8}: I t f e e ele ricall so a e 9 electrode 1mm a m n l h n th y time ture is withdrawn from said compartment.

14. Dielectric heating apparatus comprising: a

compartment for receiving therein dielectric ma terial tobeheated, a first heating electrode disposed within said compartment and connected;

said second electrode when in its saidreceiving positon being electrically isolated from said SQQ'.

and terminal, and means operative when second electrode isin its second mentioned posi-- tiontto establish an electrical connection betweensaid second electrode and said second terminal for production of a: high-frequency heating fieldv between said electrodes 15. Dielectric heating apparatus comprising a compartment forreceiving thereindielectric load material to be heated, a load tray movable into and out of said compartment including'a first heating electrode. for supporting the load ma? terial, a second heating electrode'mounted with: in said compartment and connected to one terminal of a high-frequency'source, a. second high-, frequency terminal disposed within saidcompartment spaced and insulated from said second heating electrode, and means operative to. es.-- tablishelectricalconnection between said first heatingelectrode and said second terminal upon insertion of said load tray into an operative position' in said compartment to provide a highfrequency field between said electrodes for dielectric heatin of saidload material, said means being operative to electrically isolatesaid first electrode-from said'secondterminal upon with-- drawalof said tray from its said operative p'osition.

HENRY R. WARREN.

REFERENCES CITED The following references are of record in the" 

